1. Field of the Invention
The present invention relates to a sensor mechanism-equipped catheter having a sensor portion that is disposed on a distal end of a catheter tube insertable into a living body.
2. Description of the Related Art
A catheter is a well-known medical tubular device for insertion into a body. A catheter tube, that is, a component of the catheter, has a diameter of at most several millimeters and is insertable into various passageways in a body, for example, blood vessels. In operation, a distal end of the catheter tube is guided to a desired site in a body, where a measurement (for example, blood pressure measurement and the like) or a curing operation (for example, vascular expansion and the like) is performed. Therefore, an operator of a catheter needs to unfailingly guide the distal end of the catheter tube to a desired site through external control.
Body passageways are not necessarily straight. Many passageways locally bend or divide into branches. Furthermore, body passageways are not necessarily consistent in diameter. The tube diameters of passageways may decrease, or an obstacle (for example, a blood clot) may exist in a passageway, thereby reducing the passageway diameter. Therefore, a conventional catheter having no device for detecting a situation or condition ahead in the moving direction of the catheter tube requires an operator to rely on the operator's experienced skill in order to properly operate the tube, that is, to guide the tube to a desired site.
To solve such a drawback, sensor mechanism-equipped catheters have been proposed. An example of conventional sensor mechanism-equipped catheters is shown in FIG. 10. In a sensor mechanism-equipped catheter 91, a catheter tube 92 has a pressure barrier wall 93 that is provided near a distal end of the catheter tube 92. A chip-housing chamber 94 is thereby separately formed inside the tube 92. The pressure barrier wall 93 is normally formed of a stainless steel or ceramic plate material. In the chip-housing chamber 94, a semiconductor pressure sensor chip 96 is mounted on a seat member 95 fixed in the chamber 94. The chip-housing chamber 94 is filled with a pressure-transmitting medium 97. A piston 98 for sealing the pressure-transmitting medium 97 is disposed movably on a distal end opening of the tube 92.
In the sensor mechanism-equipped catheter 91, when a pressure change occurs on the outside surface of the piston 98, which is a pressure-receiving portion, the effect of the pressure change is transmitted to the pressure-sensitive surface of the sensor chip 96 by the pressure-transmitting medium 97. In this manner, the presence of an obstacle or the like in the moving direction of the catheter tube 92 can be detected.
However, in the conventional sensor mechanism-equipped catheter 91, the catheter tube 92 has a small diameter, so that it is difficult to incorporate various small-size components, such as the sensor chip 96, the seat member 95, the pressure barrier wall 93 and the like, into the tube 92. Thus, the production of the conventional catheter 91 is not easy. Furthermore, since the aforementioned special components must be mounted in the tube 92, a normal catheter tube cannot be employed but a dedicated catheter tube must be prepared.
Normally, smaller diameters of catheters are more favorable. However, the smaller the diameter of the catheter tube 92, the more difficult it becomes to mount in the tube 92 the pressure barrier wall 93 that can reliably block flow of the pressure-transmitting medium 97. The production thus becomes more difficult. If the pressure barrier wall 93 may be able to be mounted inside the tube 92 with a reduced diameter, it is likely that a gap will form between the wall 93 and the tube 92 or the like, thereby failing to reliably sealing in the tube interior. If this happens, the pressure-transmitting medium 97 is allowed to flow toward the base end of the tube 92, so that precise pressure transmission becomes impossible and the sensing precision of the catheter 91 deteriorates. Due to this problem, size reduction must be traded for improvements in sensing precision of the conventional catheter.